Gut Microbes from People Can Transmit Obese or Lean Body Types to Mice

9/6/2013

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​A study in mice has found that gut microbes obtained from obese or lean
people, within certain dietary contexts, can transmit
obesity or leanness to mice in the lab. While there is
ample evidence that genetics and other factors play
an important role in the development of obesity, there
is also evidence that the community of bacteria living
in the gut and their collective bacterial genomes, or
“gut microbiome,” may affect and relect a person’s
health and nutritional status. For example, recent
research raised the possibility that differences in the
gut microbiome may explain why twins with identical
genetic makeups can have very different disease and
nutritional states.

A group of researchers were interested in exploring
this idea using sets of identical twins who were
“discordant” for obesity, which means one twin was
obese while the other was not. Previous research
with such discordant twins has shown that obesity
is associated with changes in the types of bacteria in
the gut; however, it is unclear whether these changes
in the gut microbiome actually contribute to the
development of obesity. To examine this possibility,
scientists transferred the gut microbiomes from twins
discordant for obesity into mice previously raised in
sterile conditions and initially free of any gut microbes.
Even though all mice were fed the same diet, only the
mice that received the obese twin’s microbiome gained
weight, while the mice that received gut microbes from
the lean twin did not.

Knowing that mice often share gut microbes with
their cage mates, the scientists housed the “lean”
mice—those inhabited by the lean human twin’s gut
microbes—together with the now “obese” mice—
those with the obese twin’s gut microbes—to see if the
microbes from one set of mice would spread to, and
affect, the other set of mice. Under these conditions,
the weights of the lean mice did not change, but after
several days the obese mice lost a signiicant amount of
weight and began to harbor the same types of bacteria
that were in the lean mice. This inding suggested
that the microbiome from the lean mice, along with its
lean-promoting effects, was being transferred to the
obese mice, but not vice versa.

When the scientists compared the microbiome from
the lean mice to that of the obese mice, they found
differences in genes that regulate metabolism,
including the metabolism of certain amino acids
(components of proteins) and effects on fats and
starches, suggesting that metabolic changes are
responsible for the microbiome’s effects on weight.
However, the protective effects of the lean twin’s
microbiome were only seen when the mice were fed a
healthy diet with high amounts of fruits and vegetables
and low amounts of saturated fat, meaning that changes
in weight were not dependent on the microbiome alone,
but were also dependent on diet.

These studies provide convincing evidence that the
gut microbiome, in conjunction with diet, can strongly
affect the ability to gain or lose weight in mice, and
may lead to insights into the role of the gut microbiome
in regulating weight in humans.